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Author Topic: Noise/QRN Problem  (Read 1508 times)

Posts: 5483


« on: June 14, 2004, 09:46:50 AM »

WD5GEY wrote:

> Please DO NOT use an AM radio to analyze noise.  

I would say to use any tool you have to find the noise.  A particularily nasty buzz I was getting between 2 to 6MHz was found by using an AM radio with a loopstick antenna.  Yes, it let me up and down the lines for a while but by triangulation and making notes on where it was the strongest, I found it in a few evenings.  The noise originated 1/4 mile from my shack, but was not copyable on my VHF aircraft receiver until I was less than a block away from it.

Mark K5LXP
Albuqerque, NM


Posts: 38

« Reply #1 on: June 13, 2004, 12:45:07 PM »

I've been in the process, over the last couple of months, of putting up a new station after several years out of the hobby.  In the past, I lived in a rural area, and QRN was never a significant problem for me.  Now I am in an urban area, and as I expected, I do have noise.  However, until now the noise blanker in my FT-890 knocked it right out.

But no more.  I am now experiencing what I can best describe as an impulse noise problem, similar to ignition noise from a car, except that the impulses, if you will, are irregular in interval, whereas the noise one might have in a car is in sync with the firing of the spark plugs and so forth.

The oddest part to me is that the problem is unmanageable during the day.  The QRN is present on all bands, and ranges from an S5 to S9 (usually the latter).  Yet as the Sun goes down and the evening comes, the noise subsides to the level that the radio's noise blanker can pretty well eliminate it.

My guess is this is some kind of electrical noise, and it does not seem to be coming from within my house, as I've tried shutting everything down in the house, and it makes no difference.

If anyone has any ideas or suggestions, they would be greatly appreciated.  Also, if you have any questions about my installation (it's still a work-in-progress), please ask.

Thanks and 73,


Posts: 144

« Reply #2 on: June 13, 2004, 01:42:05 PM »

Pat - sounds like power line noise. Had a similar problem at my QTH that was fixed by my power utility. See:

for the story. Since then had a noise pop up again which the same folks found and fixed. This time it was hardware on two poles near my home; once they were repaired the noise was gone and all is quiet again. So would recommend you contact your provider and ask them to investigate.

Additionally, you may want to check out the book "AC Power Interference Handbook" by Marv Loftness KB7KK (now in its 2nd edition and available from ARRL and others) which is a great reference (ISBN 0-9653760-3-6) for trying to figure out what your problem might be.

Good Luck!

Posts: 729


« Reply #3 on: June 13, 2004, 03:10:24 PM »

Most likely power line noise, yes.  If, though, you live near businesses, the field opens up much wider!  This is especially true if the noise abates late at night and starts again in the morning.  Older electric cash registers, adding machines, vending machines of all types, coolers, cleaning equipment, the list is almost endless.  

Grab a tiny, portable AM pocket radio and go for a walk.  (Or drive.)  You can locate the noise, whether it is on a power pole, in a business, or outdoors, such as at a car wash, gas station, etc.  

Once located, what you can do about it is another matter entirely!  

Good luck

Posts: 6252

« Reply #4 on: June 13, 2004, 05:54:35 PM »

As W5HTW said, grab an AM pocket radio and go for a walk (or ride) and see if you can find where the greatest noise concentration is.  If you can locate that, then call your power company WITH THE PARTICULARS!  Even though any power company will try to find and fix problems, if you can tell them where the noise is greatest, you will most likely get quicker satisfaction.

Also, if the noise goes up when local factories begin their day and stops when they shut down, the noise may be originating from one of them.  A few years ago in the area a cutting machine that was electronically controlled was putting out a steady amount of noise that was showing up in the lower end of the 2 meter ham band.  When the local clubs RFI committee paid them a visit, the owner was more than happy to accomodate them, it seems they were getting complaints from a few other people and their own electronically controlled machinery sometimes went haywire, and they were trying to find out why.  When the source was pinpointed and shut down, and the problems went away, the owner was so happy that he donated cash to the club and joined the club too.  He eventually got his ticket and is still active today--I talk to him occasionally.

Anyway, finding the source is important, and if you go about it in the right way there's no telling what may result.  Good luck!  

Posts: 12

« Reply #5 on: June 13, 2004, 07:26:23 PM »

   Please DO NOT use an AM radio to analyze noise.
   If any of the guys who answered you had read the
   AC Power interference Handbok they would know
   that you have to use a UHF or VHF receiver
   with a directional antenna in an AM mode.
   The noise doesn't always wind up being close.
   It can be a great distance away but started at a
   relatively high freq. caused by arcing etc.
   I am going through the same routine and did contact
   the local power company (houligans) who don't
   really care about it unless it affects multiple
   houses and people. It costs them money & time to
   investigate these things and believe me we are on
   the bottom of the list.

   I will be starting my search here in CT again
   this month to see if I can find the problem.
   The list of possibilities includes: Light
   dimmers, computers (poor filtering), BPL testing,
   arcing insulators etc., etc. I am trying to find
   a 'cheap' VHF/UHF receiver that has an AM mode
   to help with the search. I will also try AC
   line filtering directly in the main breaker box
   and anything else I can think of. If I figure
   something out I will send you an email if you'd


Posts: 9930

« Reply #6 on: June 13, 2004, 07:31:49 PM »

some of the handie talkies have an AM setting for the weather band on RX only and theat mite be of help for your am vhf

Posts: 41

« Reply #7 on: June 13, 2004, 07:57:11 PM »

That would be AM for aircraft band (118-136MHz IIRC & nav beacons at 108-118?), Weather is 162.4 to 162.55 FM just above(?) the marine VHF band, right? The point is noted in any case. A multiband (or wideband HT or a scanner Rx w/ aircraft AM capacity could be used for interference (QRM not QRN if it is man made?) in this band.

Posts: 6252

« Reply #8 on: June 14, 2004, 10:01:49 AM »

Another ham wrote:

"Please DO NOT use an AM radio to analyze noise.
If any of the guys who answered you had read the
AC Power interference Handbok they would know
that you have to use a UHF or VHF receiver
with a directional antenna in an AM mode."

Hey, what do you expect us to do?  Your suggestion is great for those with the type radio that can be easily moved around, but most of us don't have one.  A simple AM radio is not the best, but is the easiest and most available tool to use to see if you can locate a noise source.

You sound like you want us to setup a battery, rig (if we even have the needed type) and antenna on a shopping cart to walk around the local neighborhood.  We all don't have the equipment or the money to get it--hams have to make due with what we have--and a portable AM radio is something almost everyone has!

Don't take this the wrong way, but common sense has to be used here--and some of us are sadly lacking in that most important tool.

Posts: 518

« Reply #9 on: June 14, 2004, 12:00:02 PM »

A local amateur found his noise was coming from a bad neon sign decorating the perimeter of a restaurant. It was on the side that the manager could not see easily.

Some eating places are daytime only.

Ole man Jean

Posts: 1368

« Reply #10 on: June 14, 2004, 03:39:10 PM »

WD5GEY wrote:
>Please DO NOT use an AM radio to analyze noise.
>If any of the guys who answered you had read the
>AC Power interference Handbok they would know
>that you have to use a UHF or VHF receiver
>with a directional antenna in an AM mode.

I think "have to" is a little strong. One of the fundamental principles of Ham Radio is that you do the best you can with what you have available.

And by the way, a radio can be AM and VHF also. You probably meant an AM/MW broadcast receiver?

VHF radios and handheld yagis work great in this application -- that's why my local lineman has one in his truck.  Ultrasonic systems work good too for what my lineman does, but they aren't going to help THIS guy.  I agree you should have the right tools (and know how to use them) if you DF electrical noise for a living.  Having the right tools saves a lot of time.  But for a guy who's trying to find a problem RIGHT NOW that's killing his enjoyment of radio?  Use what you've got.

Lots of problems can be diagnosed without a professional sniffer.  I have found problems like light dimmers and switching power supplies just by keeping an AM portable next to me when I turn off my breakers one at a time, then walking around the house with it when I figure out which circuit the problem is on.

I found a similar regularly-pulsed 20-over-9 interference on the 70-cm satellite subband (a Radio Shack wireless thermometer) by walking around with my dual-band HT.  It wasn't right ON the satellite frequency, but it was strong enough to de-sense my satellite receiver.

I have a portable SWL receiver with a homebrew shielded loop antenna that I use to diagnose things when they crop up in the neighborhood.  Not VHF, but it works well enough to find the nasty ones for me.  One was a couple of blocks away, but once I got the general direction, I was able to cruise the neighborhood to narrow it down by setting my AM car radio between stations and noting where the noise was loud and where it wasn't.  Again, an AM broadcast receiver --the car radio-- helped. The final Direction Finding, down to the individual house, was done once again with the loop, but it wasn't VHF.

It all depends on the noise.  The sniffer uses VHF because it's listening for a far-enough removed harmonic that you probably have to get CLOSE to hear it.  It doesn't mean that using an AM broadcast receiver NEVER works--it might work well enough to get this guy started.  The worst thing that can happen is that the noise really IS VHF and he can't hear it at the lower frequencies.  Nothing ventured, nothing gained.

He could wait and put up with the noise till he buys exactly the right gear, something he might use only once, or he could attack the problem right now with what he has.

Or should I give up DXing till I can afford an IC-7800 and stacked monobanders?  Shoot, here I was having fun all along.  I didn't know there were better tools for the job...

Posts: 38

« Reply #11 on: June 14, 2004, 07:41:37 PM »

As regards to the AM radio vs VHF, etc, I have a small Sony general coverage receiver that I took out into the yard yesterday, set it on 20m, and sort of moved around a bit.  The noise can be heard on the Sony, all right, but I think I'm going to have to rig up a loop antenna for it.  I'm also going to try the drive around the neighborhood thing tomorrow.

Now here is another interesting aspect to all this, as regards to various sources of noise.  In the morning, up until around 1000 or so, the noise starts to come up, but my noise blanker can clear it without much difficulty.  

But much after 1000, the noise level jumps up to S9+, and you might as well hang it up.  And as I mentioned in the earlier post, but probably didn't make clear, when evening comes on, the noise fades out, until it's pretty well gone after about 2100 or so.  You can still hear it a little, but it's hardly noticeable.

And for another interesting twist, yesterday afternoon, right after I finished wandering around outside with the Sony, I checked the bands again. I was on 15m at the time, was able to work this guy up in the Boston area, and while I talked to him, we got ourselves a good frog strangler of a rain.  When the QSO ended, I noticed that the noise had not faded out, but was GONE, completely.  Dead quiet on all bands.

Then this morning as usual, the noise starts up again, gradually getting worse until the rig is basically unusable past 1030 or so.

Based on all this, I have no doubt it's electrical in nature, but the symptoms are damned unusual.  If anyone has any further insights about this, especially with these latest revelations, I'd love to hear them.

Thanks to all of you all, and 73


Posts: 1368

« Reply #12 on: June 14, 2004, 10:19:29 PM »

Pat, I think you're on the right track.

First, see if it's in your house.
If it's not, see if you can find out WHERE it is.
You've done #1.  Now do #2.

Where it is is probably the key to finding WHAT it is.
If it's not in your own care, custody, and control, WHAT it is might not matter, depending on your relationship with the "owner" of the problem.

Don't fret the noise blanker issue.  Noise blankers are all designed to do different things.  Some are designed only to take out spark-plug type impulse noises.  Depending on whether your rig was designed and built during the "woodpecker" period, it might do other things.

The fact that it gets stronger depending on time of day is interesting, but not necessarily diagnostic.  The most obvious is that it's probably thermally-related.  An insulator maybe, that gets better or worse with temperature.  But there are a lot of other things that change with time of day.  Don't get tunnel vision.  Consider all possibilities.

Do that drive around the neighborhood.  Although it COULD be coming from somewhere else, the Law of Parsimony says that it's probably not.  Find the vicinity.  Then build that loop and triangulate on the actual house.  From there on, it's all up to your "people" skills.  Finding it is one thing.  Getting a total stranger to own the problem and fix it is a whole other thing.
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